Solved – How to set up a two-way mixed ANOVA with a covariate in SPSS

ancovarepeated measuresspss

I wanted to carry out a two-way ANCOVA for my data. However, SPSS isn't liking that I have only one IV.

I have

  • One IV: Group (3 levels, i.e. 2 experimental groups and a control group),
  • One DV: outcome measure (2 levels, i.e. time 1 and time 2),
  • One covariate (I have checked and this demographic continuous variable moderately correlates with the DV).

Please could someone help as to whether I am missing something in terms of putting this into SPSS?

Best Answer

I am guessing that you have your data in wide format. This seems to be causing you confusion because in wide format it is less obvious that "time" is your second independent variable.

One option in SPSS for doing what it sounds like you want to do:

  1. Analyze -- GLM -- Repeated Measures
  2. Enter time as repeated measures factor with two levels
  3. Enter Group as a between subjects factor
  4. Enter the dependent variable (presumably represented as two variables in SPSS as your two times points)
  5. Enter your covariate in the covariate box

For more information, see Andy Field's SPSS Repeated Measures tutorial.

However, given that repeated measures ANOVA already controls for individual differences in some respect, you may want to think about the meaning of including a time-invariant covariate in such a model. See here for a discussion of the issues related to covariates in repeated measures ANOVA.

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